This invention relates to seals for defining a scroll compressor back pressure chamber wherein the contact pressure between the seal and the scroll member is reduced compared to the prior art.
Scroll compressors are widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members face each other. The two scroll members each have a base with a generally spiral wrap extending from the base. The two spiral wraps interfit to define compression chambers. One scroll member is driven to orbit relative to the other. As the one scroll member orbits relative to the other, the intermitting spiral wraps move and decrease the volume of the compression chambers. In this way, refrigerant is compressed.
While scroll compressors do have several advantages, they also raise many design challenges. As an example, a separating force is created between the two scroll members as the refrigerant is compressed. The separating force tends to move the two scroll members away from each other. This reduces sealing contact between the two scroll members and leads to efficiency losses.
To address the separating force, scroll compressor designers create a "back pressure" chamber behind one of the two scroll members. Compressed fluid is tapped to the back pressure chamber and creates a force which opposes the separating force. The back pressure chamber is defined behind the base of one of the two scroll members by inner and outer sealing surfaces.
In one type of scroll compressor, the back pressure chamber is defined behind the orbiting scroll member, and includes two separate seals, with one at a radially inner position and one at a radially outer position. Pressurized refrigerant is tapped to a chamber defined between the two seals and creates the back pressure force.
In another type scroll compressor, the back pressure chamber is defined behind the non-orbiting scroll, and a single large seal with two sealing areas is utilized. The present invention has more benefit to the first type scroll compressor; however, aspects of the present invention may also prove beneficial to the second type scroll compressor.
The first type scroll compressor is shown in FIG. 1. A scroll compressor 20 incorporates a crankcase 22 receiving an orbiting scroll member 24. A pair of seals 26 and 28 define a back pressure chamber 30. A fixed scroll member 32 is positioned opposed to the orbiting scroll member. While the present invention is shown with the back pressure chamber defined behind the orbiting scroll 24, it should be understood that aspects of this invention might also apply to scroll compressors having the back pressure chamber defined behind the fixed, or non-orbiting scroll member. Further, while a pair of seals are shown, aspects of this invention might apply to scroll compressors having a single large seal.
As shown in FIG. 2A, seals 26 and 28 include a seal jacket 30 having a rear wall 32, and inwardly extending lips 34 and 36. A coil spring 38 is positioned in each seal jacket. The seal portions 34 abut a rear surface 40 of the orbiting scroll member 24. The spring 38 tends to bias the lip 34 into contact with the scroll member rear surface 40.
A gas pressure force on the seal jacket 34 also forces the seal jacket 34 into rear surface 40, in addition to the coil spring 38. As shown in FIG. 2B, inward of lips 34 and 36, the lips see the full pressure P in the back pressure chamber 30. However, outwardly of the lips 34 and 36, there is a restriction against flow. Thus, there is a pressure gradient from P downwardly toward a lower pressure. As shown in FIG. 2C, there is a gradient of the contact force between the lip 34 and 36 and the rear surface 40 of scroll member 24 which is generally reversed from the gradient shown in FIG. 2B. As shown, the force is very large adjacent the rear wall 32, and becomes smaller adjacent the inner edges of lips 34 and 36. Adjacent the inner edges of lips 34 and 36, the pressure outwardly of the lips is generally equal to the pressure inwardly, and thus the pressures are cancelled. However, due to the pressure gradient the contact force does become larger approaching the rear wall 32.
Thus, adjacent the rear wall 32, there is a contact force against the rear surface 40 which is undesirably high. Orbiting scroll 24 orbits relative to the seals. This contact force can lead to undue seal wear and premature seal failure.